1. Field of the Invention
The present invention relates to novel hydrated strontium fluosilicates which are activated with divalent europium and are useful as black light emitting luminescent materials.
2. Description of the Prior Art
Divalent europium is a well known activator for luminescent materials and it typically produces wide band emission in the visible or in the near ultraviolet regions of the spectrum. However, compounds activated with divalent europium and which exhibit a narrow band in the near ultraviolet region have already been proposed to this art. Thus, the U.S. Pat. No. 3,630,945 describes alkaline earth fluoaluminates which are activated with divalent europium and which exhibit a sharp line ultraviolet emission spectrum which is characteristic of 4f to 4f energy level transitions. Nonetheless, this spectrum exhibits the disadvantage of a broadening of the base of the emission peak which results from an emission which is due to 5d and 4f transitions. This proves to be troublesome for any application requiring a spectral separation of a very narrow emission.
And in U.S. Pat. No. 4,122,349, assigned to the assignee hereof, there are disclosed novel luminophors having high fluorescent intensity, and characterized by a sharp line spectrum having a very narrow peak in the near ultraviolet region. Such luminophors are anhydrous alkaline earth metal fluosilicates activated with divalent europium and corresponding to the general forumla M.sub.1-x Eu.sub.x.sup.2+ SiF.sub.6 wherein M is a member selected from the group consisting of strontium, barium and mixtures thereof, and wherein 0&lt;x.ltoreq.0.2.